Histamine is widely, if unevenly, distributed throughout the animal kingdom and is present in many venoms, bacteria, and plants

Histamine is widely, if unevenly, distributed throughout the animal kingdom and is present in many venoms, bacteria, and plants.

• Histamine is widely, if unevenly, distributed throughout the animal kingdom and is present in many venoms, bacteria, and plants.

Immunologic release

• Immunologic release

• histamine plays a central role in immediate hypersensitivity and allergic responses
• The release of histamine only partially explains the biological effects that ensue from immediate hypersensitivity reactions

• Chemical and mechanical release

• Tubocurarine, succinylcholine, morphine

Mechanism of action

• Mechanism of action

• Tissue and organ system effect

• Nervous system
• Cardiovascular system
• Bronchial smooth muscle
• Gastrointestinal tract smooth muscle
• Other smooth muscle organs
• Secretary tissue
• Metabolic effects
• The triple response
• Other effects possibly mediated by histamine

regulation of drinking

• regulation of drinking

• body temperature

• secretion of antidiuretic hormone

• control of blood pressure

• perception of pain

• wakefulness

Vasodilation

• Vasodilation

• Increased "Capillary" Permeability

• Triple Response of Lewis

• Heart

• Histamine Shock

Contraction is due to activation of H1 receptors

• Contraction is due to activation of H1 receptors

• relaxation (for the most part) is due to activation of H2 receptors

regulator of gastric acid secretion

• regulator of gastric acid secretion

Pain

• Pain

• Itch

Clinical use

• Clinical use

• a diagnostic agent
• to assess nonspecific bronchial hyperreactivity in asthmatics
• as a positive control injection during allergy skin testing

• Toxicity and contraindications

• Flushing, hypotension,tachycardia, headache wheals, brochoconstriction, gastrointestinal upset

H1 receptor antagonists

• H1 receptor antagonists

• H2 receptor antagonists

Absorption, distribution

• Absorption, distribution

• Metabolism:

• Astemizole and Terfenadine

Smooth Muscle

• Smooth Muscle

• Capillary Permeability

• Flare and Itch

• Immediate Hypersensitivity Reactions

• Central Nervous System

• Can both stimulate and depress the CNS

Histamine receptor blockade

• Histamine receptor blockade

• Other actions

• Sedation
• Antinausea and antiemetic actions
• Antiparkinsonism effects
• Antichlinoceptor effect: Promethazine
• Adrenoceptor blocking action
• Serotonin blocking action
• Local anesthesia: Promethazine

Clinical use

• Clinical use

• Allergic reaction
• Motion sickness and vestibular disturbance
• Nausea and vomiting of pregnancy?

• Toxicity

• Sedation, antimuscarninc action,
• Drug allergy
• Drug interaction
• Teratogenic effects

Despite persistent popular belief, H1 antagonists are without value in combating the common cold.

• Despite persistent popular belief, H1 antagonists are without value in combating the common cold.

Mechanism of action

• Mechanism of action

Serotonin agonists

• Serotonin agonists

• Serotonin antagonists

Phenoxybenzamine (5HT2)

• Phenoxybenzamine (5HT2)
• Cyproheptadine (5HT2)
• Ketanserin (5HT1C)
• Odansetrone (5HT3)

Sertonin related to sleep, emotion, sex, and appetite

• Sertonin related to sleep, emotion, sex, and appetite

• Could reduce food intake

• Fenfluramine, dexfenfluramine
• Cause serotonin release and inhibition of food uptake

• Toxicity:

• fatal and nonfatal pulmonary hypertension
• Valvular lesions